JP2011141204A - Battery voltage detection circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery voltage detection circuit that can accurately detects a voltage of a battery at a time when the voltage is varied. <P>SOLUTION: This battery voltage detection includes a first capacitor 10, an operational amplifier 12 having a non-inverting input terminal (+) of which keeps a reference voltage VREF applied, a second capacitor 11 which is connected across the output terminal of the operational amplifier 12 and the inverting input terminal (-) thereof, and a switch circuit. After the switch circuit respectively applies voltages of both terminals of batteries BV1 to BV4 to one terminal and the other terminal of the first capacitor 10, the switch circuit connects one terminal of the first capacitor 10 to the inverting input terminal (-) of the operational amplifier 12, and then it applies the reference voltage VREF to the other terminal of the first capacitor 10. The voltages of both terminals of the batteries BV1 to BV4 are detected on the basis of the output voltage VOUT of the operational amplifier 12. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a battery voltage detection circuit.

  In various devices and chargers using rechargeable batteries such as lithium ion batteries, it is necessary to accurately detect the voltage of each battery in order to manage charging and discharging of a plurality of batteries connected in series.

  FIG. 5 is a circuit diagram of a conventional battery voltage detection circuit 20. The battery voltage detection circuit 20 is a circuit that detects each voltage of the batteries BV1 to BV4 connected in series, and includes a first capacitor 10, a second capacitor 11, an operational amplifier 12, and a reference voltage source 13 that generates a reference voltage VREF. The switch control circuit 14 outputs a control signal for controlling on / off of the switches SW0 to SW5 and the switches SW0 to SW5. The battery voltage detection circuit 20 has an advantage that the operational amplifier 12 does not need to have a high breakdown voltage because the first capacitor 10 is connected to the inverting input terminal (−) of the operational amplifier 12 and no DC voltage is applied.

  The operation of the battery voltage detection circuit 20 will be described based on the timing chart of FIG. In FIG. 6, the H level of the control signal applied to the switches SW0 to SW5 corresponds to the on state, and the L level corresponds to the off state. First, in the initial state (time t0), the switches SW0 to SW4 are turned off and the switch SW5 is turned on. At this time, since the output terminal and the inverting input terminal (−) of the operational amplifier 12 are short-circuited by the switch SW5, the operational amplifier 12 becomes an amplifier having a gain of 1, and the reference voltage VREF applied to the non-inverting input terminal (+) is received. Output as the output voltage VOUT.

  Thereafter, when the switch SW4 is turned on at time t1, the voltage V4 of the positive terminal of the battery BV4 is applied to one terminal of the first capacitor 10. That is, the voltage VC1 applied between both terminals of the first capacitor 10 is VC1 = V4−VREF. At this time, assuming that the capacitance value of the first capacitor 10 is C1, charges QC1 and QC1 = (V4−VREF) · C1 are accumulated in the first capacitor 10. At this time, since both terminals of the second capacitor 11 have the same voltage VREF, the charge QC2 of the second capacitor 11 is zero.

  Thereafter, at time t2, the switches SW4 and SW5 are turned off. At time t3, when the switch SW3 is turned on, the voltage at one terminal of the first capacitor 10 drops from V4 to the voltage V3 at the negative terminal of the battery BV4. Thereby, a current flows from the output terminal of the operational amplifier 12 through the second capacitor 11, the first capacitor 10, and the switch SW3. In this case, the charge QC1 stored in the first capacitor 10 is QC1 = (V3−VREF) · C1. Further, the electric charge QC2 accumulated in the second capacitor 11 by the current becomes QC2 = (VOUT−VREF) · C2.

Before and after the switch SW3 is turned on, QC1 + QC2 which is the sum of the charge QC1 of the first capacitor 10 and the charge QC2 of the second capacitor 11 is stored according to the charge conservation law. Therefore, the following equation holds.
(V4-VREF) * C1 = (V3-VREF) * C1 + (VOUT-VREF) * C2
Solving this equation for VOUT, VOUT = (V4−V3) · C1 / C2 + VREF. (V4-V3) is a voltage between both terminals of the battery BV4. The voltage VC2 applied to both terminals of the second capacitor 11 is VC2 = (V4−V3) · C1 / C2.

  Next, at time t4, the switch SW5 is turned on. Since the output terminal and the inverting input terminal (−) of the operational amplifier 12 are short-circuited again via the switch SW5, the output voltage VOUT of the operational amplifier 12 is VOUT = VREF. In the following, the voltages of the batteries BV3, BV2, and BV1 can be sequentially detected by repeating the same procedure.

JP 2008-145180 A

  By the way, the voltage of each battery may fluctuate when a large current flows through the devices connected to the batteries BV1 to BV4 described above. In this case, the conventional battery voltage detection circuit 20 detects the difference between the voltages VC1 charged in the first capacitor 10 at two different points in time, and therefore detects an accurate voltage when the battery voltage fluctuates. There was a problem that it was not possible.

  This problem will be described with reference to the timing chart of FIG. 7 by taking as an example the case of detecting the voltage (V4-V3) between both terminals of the battery BV4. In FIG. 7, the H level of the control signal applied to the switches SW3 to SW5 corresponds to the on state, and the L level corresponds to the off state. First, FIG. 7A shows a case where there is no change in V4 and V3. (V4 = V4a, V3 = V3a) In this case, the output voltage VOUT of the operational amplifier 12 is VOUT = (V4a−V3a) · C1 / C2 + VREF.

  FIG. 7B shows a case where V4 drops from V4a to V4b and V3 drops from V3a to V3b between times t3 and t4. In this case, when the switch SW4 is on, the voltage V4a is charged to the first capacitor 10, and then, when the switch SW4 is turned off and the switch SW3 is turned on, V4 = V4a and V3 = V3a. The output voltage VOUT is a normal voltage of VOUT = (V4a−V3a) · C1 / C2 + VREF. However, when V4 drops to V4b and V3 drops to V3b during the period when the switch SW3 is on, the operational amplifier 12 outputs the output voltage VOUT corresponding to the difference between V4a and V3b, (V4a−V3b). , VOUT = (V4a−V3b) · C1 / C2 + VREF. This is a voltage larger than the voltage corresponding to (V4a-V3a) or (V4b-V3b) which should be output originally.

  FIG. 7C shows a case where V4 rises from V4a to V4b and V3 rises from V3a to V3b between times t3 and t4. In this case, contrary to the case of FIG. 7C, the output voltage VOUT becomes a voltage smaller than the voltage corresponding to (V4a-V3a) or (V4b-V3b).

  Further, as described above, in the battery voltage detection circuit 20, when the switch SW4 is turned on, the voltage VC1 applied across the first capacitor 10 is VC1 = V4−VREF. In the case of a lithium ion battery, the voltage of one battery BV1 to BV4 is close to 4.5V, for example, about 4.2V, but when these are connected in series, V4 = about 16.8V. Since VREF is normally set to about 1V, VC1 = 1V becomes a high voltage of about 15.8V. Therefore, there is a problem that the first capacitor 10 needs to have a high breakdown voltage.

  Therefore, an object of the present invention is to detect an accurate voltage at that time even when the voltage of the battery fluctuates, and to eliminate the need to increase the breakdown voltage of the first capacitor.

  The present invention has been made in view of the above problems, and includes a first capacitor, an operational amplifier in which a reference voltage is applied to a first input terminal, an output terminal of the operational amplifier, and a second input of the operational amplifier. A voltage of both terminals of the second capacitor connected between the terminals and the battery is simultaneously applied to one terminal and the other terminal of the first capacitor, and then one terminal of the first capacitor is A switch circuit connected to the second input terminal of the operational amplifier and then applying the reference voltage to the other terminal of the first capacitor, and both terminals of the battery based on the output voltage of the operational amplifier The voltage is detected.

  According to the battery voltage detection circuit of the present invention, since the voltage at both terminals of the battery is applied to the first capacitor at the same time, even when the voltage of the battery fluctuates, an accurate voltage at that time is detected. be able to. Further, even when a plurality of batteries are connected in series, the voltage applied to both terminals of the first capacitor is the voltage of each battery, so that it is not necessary to make the first capacitor have a high breakdown voltage.

It is a circuit diagram of a battery voltage detection circuit according to an embodiment of the present invention. FIG. 5 is a timing diagram illustrating an operation of the battery voltage detection circuit according to the embodiment of the present invention. It is a figure explaining operation | movement of the battery voltage detection circuit by embodiment of this invention. It is a figure explaining operation | movement of the battery voltage detection circuit by embodiment of this invention. It is a circuit diagram of the conventional battery voltage detection circuit. It is a timing diagram explaining operation | movement of the conventional battery voltage detection circuit. It is a timing diagram explaining the problem of the conventional battery voltage detection circuit.

  Next, a battery voltage detection circuit 100 according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of the battery voltage detection circuit 100. The battery voltage detection circuit 100 is a circuit that detects each voltage of the batteries BV1 to BV4 connected in series, and includes a first capacitor 10, a second capacitor 11, an operational amplifier 12, and a reference voltage source 13 that generates a reference voltage VREF. , An integrated circuit including a switch control circuit 15 that outputs a control signal for controlling on / off of the switches SW0 to SW7 and the switches SW0 to SW7.

  In the operational amplifier 12, the reference voltage VREF output from the reference voltage source 13 is applied to the non-inverting input terminal (+). The reference voltage source 13 is, for example, a band gap type reference voltage source. In this case, the reference voltage VREF is about 1V. Between the output terminal of the operational amplifier 12 and the inverting input terminal (−), one and the other terminals of the second capacitor 11 are respectively connected. The output voltage VOUT of the operational amplifier 12 is input to the AD converter 16 and converted into digital data. The AD converter 16 may be built in the integrated circuit of the battery voltage detection circuit 100.

  The switch SW4 has one end connected to one terminal of the first capacitor 10 and the other end connected to the plus terminal (voltage V4) of the battery BV4 via the terminal P4. The switch SW3n has one end connected to the other terminal of the first capacitor 10, and the other end connected to the negative terminal of the battery BV4 and the positive terminal (voltage V3) of the battery BV3 via the terminal P3. That is, when the switches SW4 / SW3n are simultaneously turned on, the voltages V4 and V3 at both terminals of the battery BV4 are simultaneously applied to both terminals of the first capacitor 10, respectively.

  Similarly, one end of the switch SW3p is connected to one terminal of the first capacitor 10, and the other end is connected to the negative terminal of the battery BV4 and the positive terminal (voltage V3) of the battery BV3 via the terminal P3. . The switch SW2n has one end connected to the other terminal of the first capacitor 10, and the other end connected to the negative terminal of the battery BV3 and the positive terminal (voltage V2) of the battery BV2 via the terminal P2. That is, when the switches SW3p / SW2n are turned on at the same time, the voltages V3 and V2 at both terminals of the battery BV3 are simultaneously applied to both terminals of the first capacitor 10, respectively.

  Similarly, one end of the switch SW2p is connected to one terminal of the first capacitor 10, and the other end is connected to the negative terminal of the battery BV3 and the positive terminal (voltage V2) of the battery BV2 via the terminal P2. . The switch SW1n has one end connected to the other terminal of the first capacitor 10, and the other end connected to the negative terminal of the battery BV2 and the positive terminal (voltage V1) of the battery BV1 via the terminal P1. That is, when the switches SW2p / SW1n are simultaneously turned on, the voltages V2 and V1 at both terminals of the battery BV2 are simultaneously applied to both terminals of the first capacitor 10, respectively.

  Similarly, one end of the switch SW1p is connected to one terminal of the first capacitor 10, and the other end is connected to the negative terminal of the battery BV2 and the positive terminal (voltage V1) of the battery BV1 via the terminal P1. . The switch SW0 has one end connected to the other terminal of the first capacitor 10 and the other end connected to the negative terminal (voltage V0) of the battery BV1 via the terminal P0. That is, when the switches SW1p / SW0 are simultaneously turned on, the voltages V1 and V0 of both terminals of the battery BV1 are applied to both terminals of the first capacitor 10 at the same time.

  The switch SW6 has one end connected to the other terminal of the first capacitor 10 and the other end connected to the inverting input terminal (−) of the operational amplifier 12. The switch SW7 has one end connected to one terminal of the first capacitor 10 and the other end connected to the non-inverting input terminal (+) of the operational amplifier 12. The switch SW5 is connected as a feedback capacitor between the output terminal of the operational amplifier 12 and the inverting input terminal (−).

  The switch control circuit 15 can control on / off of the switches SW0 to SW7 based on a signal input from the microcomputer. It is also possible to realize a function equivalent to that of the switch control circuit 15 by software.

  Next, the operation of the battery voltage detection circuit 100 will be described based on FIG. 2, FIG. 3, and FIG. FIG. 2 is a timing diagram of the battery voltage detection circuit 100. The H level of the control signal applied to the switches SW0 to SW7 corresponds to the on state, and the L level corresponds to the off state. 3 and 4 are circuit diagrams illustrating an operation for detecting a voltage (V4-V3) between both terminals of the battery BV4.

  First, the operation when the voltage (V4-V3) between both terminals of the battery BV4 is detected will be described. First, in the initial state (time t0), the switch SW5 is turned on, and the other switches SW6, SW7, SW4 / SW3n, SW3p / SW2n, SW2p / SW1n, and SW1p / SW0 are turned off. At this time, since the output terminal and the inverting input terminal (−) of the operational amplifier 12 are short-circuited by the switch SW5, the operational amplifier 12 becomes an amplifier having a gain of 1, and the reference voltage VREF applied to the non-inverting input terminal (+) is received. Output as the output voltage VOUT. (See Fig. 3 (a))

  Thereafter, when the switches SW4 / SW3n are simultaneously turned on at time t1, the voltage V4 is applied to one terminal of the first capacitor 10, and the voltage V3 is simultaneously applied to the other terminal. At this time, the voltage VC1 applied between both terminals is (V4-V3). Further, assuming that the capacitance value of the first capacitor 10 is C1, charges QC1 and QC1 = (V4−V3) · C1 are stored in the first capacitor 10. On the other hand, the voltage VC2 applied between both terminals of the second capacitor 11 is 0V, and the charge QC2 stored in the second capacitor 11 is 0. (See Fig. 3 (b))

  Thereafter, at time t2, the switches SW4 / SW3n and SW5 are turned off. As a result, the first capacitor 10 is electrically disconnected and enters a floating state, but the voltages at both terminals thereof remain at V4 and V3, respectively, and the charges QC1 and QC2 remain unchanged. (See Fig. 3 (c))

  At time t3, the switch SW6 is turned on. As a result, the other terminal of the first capacitor 10 is connected to the inverting input terminal (−) of the operational amplifier 12. At this time, since the voltage of the inverting input terminal (−) becomes VREF due to an imaginary short, the voltage of the other terminal of the first capacitor 10 also changes from V3 to VREF. Along with this, the voltage at the other terminal of the first capacitor 10 changes by (V3−VREF), and thus becomes (V4−V3) + VREF. The charges QC1 and QC2 are unchanged. (See Fig. 4 (a))

  Thereafter, at time t4, the switch SW7 is turned on. Then, a current flows from the output terminal of the operational amplifier 12 to the reference voltage source 13 through the second capacitor 11, the switch SW6, the first capacitor 10, and the switch SW7. In this case, since the voltage at both terminals of the first capacitor 10 is VREF, the charge QC1 is zero. Further, the electric charge QC2 accumulated in the second capacitor 11 by the current becomes QC2 = (VOUT−VREF) · C2. C2 is a capacitance value of the second capacitor 11. (See Fig. 4 (b))

  Before and after the switch SW7 is turned on, QC1 + QC2 which is the sum of the charge QC1 of the first capacitor 10 and the charge QC2 of the second capacitor 11 is stored according to the charge conservation law. Therefore, the following equation holds.

(V4-V3) .C1 = (VOUT-VREF) .C2
Solving this equation for VOUT, VOUT = (V4−V3) · C1 / C2 + VREF. That is, the same result as that of the conventional circuit is obtained as the output voltage VOUT.

  After that, at time t5, the switches SW6 and SW7 are turned off and the switch SW5 is turned on to return to the initial state again. As a result, the output voltage VOUT of the operational amplifier 12 returns to VREF again. Thereafter, by repeating the same procedure, the voltages of the batteries BV3 to BV1 can be sequentially detected.

  According to the battery voltage detection circuit 100 described above, since the voltages of both terminals of the batteries BV1 to BV4 are sequentially applied to the first capacitor 10 at the same time, even when the voltages of the batteries BV1 to BV4 fluctuate, An accurate voltage at the time can be detected. Further, since the voltage applied to both terminals of the first capacitor 10 is the voltage of each battery, it is not necessary to make the first capacitor 10 have a high breakdown voltage.

  Needless to say, the present invention is not limited to the above-described embodiment, and modifications can be made without departing from the scope of the invention. For example, the number of batteries BV1 to BV4 connected in series can be changed. In that case, the number of switches is changed according to the number of batteries.

  Further, the present invention can be applied even if the number of batteries is only one, for example, only the battery BV4. In that case, the switches SW4 / SW3n, SW5, SW6, and SW7 may be used as the switches.

  Further, by providing the operational amplifier 12 and the switches SW5 to SW7 corresponding to each battery, it is also possible to detect the voltage of each battery at the same time.

Furthermore, the switch control circuit 15 can select a desired battery, and simultaneously detect the voltage of each battery based on the voltage of the selected battery.

  Further, the switch control circuit 15 can select one battery from the batteries BV1 to BV4 and detect the voltage of the selected battery.

10 first capacitor 11 second capacitor 12 operational amplifier 13 reference voltage source 15 switch control circuit 16 AD converter

Claims (5)

A first capacitor;
An operational amplifier having a reference voltage applied to the first input terminal;
A second capacitor connected between an output terminal of the operational amplifier and a second input terminal of the operational amplifier;
After simultaneously applying the voltage across the battery to one terminal and the other terminal of the first capacitor, respectively, one terminal of the first capacitor is connected to the second input terminal of the operational amplifier; And a switch circuit that applies the reference voltage to the other terminal of the first capacitor, and detects a voltage across the battery based on an output voltage of the operational amplifier.   The switch circuit selects a plurality of batteries connected in series one by one, and applies voltages across the selected batteries to one terminal and the other terminal of the first capacitor, respectively. The battery voltage detection circuit according to claim 1.   The switch circuit selects one battery from a plurality of batteries connected in series, and simultaneously applies a voltage across the selected battery to one terminal and the other terminal of the first capacitor, respectively. The battery voltage detection circuit according to claim 1.   4. The battery voltage detection circuit according to claim 1, wherein a capacitance value of the second capacitor is larger than a capacitance value of the first capacitor. 5.   The battery voltage detection circuit according to claim 1, further comprising an AD converter that converts an output voltage of the operational amplifier into digital data.

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